The present invention relates to a panel type color display device and a system for processing the image information, and more particularly, the invention relates to a panel type color display device of the class wherein there are provided a display portion consisting of a plurality of pixels, of which each is driven in response to the image information to vary the light transmittance thereof, and backlight sources, of which each can be independently on-off controlled in response to the image information to emit a color light in red (R), green (G), or blue (B), and also relates to a system for processing the image information.
In recent years, apparatus for office automation use such as personal computers, and home electronic products like television sets have been made more compact, of lighter weight, and thinner shaped to a great extent. This tendency is reflected in the field of the display device, and causes the same demand for the display device. In order to meet this demand, various efforts are now being paid to develop a flat panel type display device of lighter weight and thinner shape like a liquid crystal display (LCD) as a device capable of being used in place of prevailing conventional CRT's (cathode ray tubes).
As one of technological demands for these flat panel type display devices, there is a demand for achievement of the full color display. For instance, the color liquid crystal display (LCD) of the thin film transistor system (TFT) realizes the color display by adopting the active matrix system. According to this TFT system, the dot driving is carried out on the dot by dot basis, so that the high duty dot driving can be obtained by making use of the memory effect of condensers respectively associated with dots, thereby providing the LCD that can display color images with excellent contrast. However, this system never fails to require a lot of TFT's satisfying the VGA specification, thus inevitably resulting in not only pushing up the manufacturing cost, but also lowering the manufacturing yield. Further, what is worse, this point is still remaining as an unsolved problem up to now without finding any effective solution.
On one hand, the super twisted nematic system (STN) has succeeded in realizing a low cost color LCD by means of adopting the simple matrix system. In this case, however, the speed of frame display is not so fast that color mixture is apt to take place, thus still leaving the problem to be solve as to its poor contrast. In order to solve this problem and to realize the color display with fine contrast at the high-speed frame display, there have been proposed various driving systems as countermeasures for obviating such problem, for instance the double matrix electrode driving system, the time sharing driving system, and so forth. Furthermore, there have been proposed the active addressing driving system that tries to realize the fine contrast and the high-speed frame display without reducing the resolution, by dispersing small pulses instead of large selecting pulses and performing simultaneous scanning of all the lines.
Regardless of the TFT system or the STN system, most of conventional LCD's are adopting a color filter system comprising filters of 3 primary colors R, G, and B. In case of displaying in color R, the region for color R is made light transmissible while the other regions for G and B are made not. In case of the color filter system, however, as will be easily understood, respective color regions of R, G, and B require proper pixels corresponding thereto, so that 3 times pixels of the monochromatic display have to be driven for full color display. Therefore, in order to obtain an image with high resolution, there are required the finest precision machining, the sophisticated technology for driving pixels, and the color filters having the improved light transmittance. Moreover, there has to be solved the difficult issue of color balance adjustment in the display. As mentioned above, there are embraced in the color filter system a lot of problems that have to be obviated by solving thereof.
In view of the situation of the prior art LCD as described in the above, there has been recently proposed such a panel type color LCD adopting the 3 color backlight system as disclosed in JPA No. Hei 4 (1992)-338996. In the color LCD of this type, there are provided 3 independent light sources of which each is specifically assigned to emit a color light of R, G, or B, and is turned on in order at a predetermined period. Thus, the full color display can be obtained by applying color signals to corresponding pixels in synchronization with said period of turning on the light sources.
According to the conventional color filter system, it is possible to process color signals of R, G, and B as parallel data. For instance, if it is desired to display the image of high brightness with the R-signal, regardless of behaviors of G or B signals, it is possible to overwrite the image data on the R region of pixels by making use of the memory effect due to the condensers of the LCD driving circuit. Thus, the color video can be easily obtained with high contrast.
However, according to the 3 color backlight system, the color image information is once converted into the serial data in which the image information corresponding to respective colors R, G, and B, are switched at a predetermined period, and then, the backlight sources of R, G, and B, are sequentially turned on in synchronization with the switching period of said serial data, thereby realizing the full color image display. Therefore, as shown in FIG. 11, even though it is desired to obtain the image of high brightness with the R-signal and the liquid crystal in a predetermined pixel region is driven with said R-signal to turn it on, this ON-state of the liquid crystal with R-signal is soon erased by the G-signal or B-signal in the next period, so that it is hardly possible to obtain the adequately high quantity of the transmitting light, thus the color image with high contrast being not obtainable. Especially, this operational characteristics remarkably appears in case of realizing the color display by means of the STN system, so that it has been very much desired to promptly solve this problem.
The present invention has been made in view of the various problems as described in the above, which would never fail to come out in the course of realizing the panel type color display according to the 3 color backlight system. Accordingly, an object of the present invention is to provide a novel and improved panel type color display device which is most suitably adaptable especially to the LCD of the STN system, and in which signals for driving pixels are so improved that the frame response of respective pixels is enhanced and the color image can be obtained with high contrast.
Another object of the present invention is to provide a novel and improved panel type color display device in which the image information is developed at a high speed, and the speed of transmitting information to the LCD is made much faster.